Selenite (chemical formula: CaSO4Â·2H2O) is a hydrous calcium sulfate, meaning it is composed of oxygen, sulfur, hydrogen, calcium and water. It is basically a glassy, well-crystallized form of gypsum and is often referred to as satin spar.
Selenite is soft, and can easily be scratched with a fingernail. The thin crystals can be slightly flexible, but will snap if bent too far. Some crystals found in Kentucky have grown in severely curved patterns and flower-like petals.
In some very...